Why does static pressure decrease as CFM increases on blower fan charts?

[hali24953]

Hi, Looking at blower fan charts, why does the static pressure drop with increased CFM, what makes sense to me should be a pressure difference rise with increasing CFM.

 

[russ_watters]

Welcome to PF!

The pressure required to blow air through a ductwork system rises with increasing airflow. But fans aren't ductwork. For a fan, the greater the resistance, the lower their airflow.

 

[hali24953]

Thanks!
Does that mean that fan charts tell what CFM flow will the fan be able to give at a given resistance to its inflow?
The resistance coming from a pipe wall for example, a fan at the outlet will be able to suck the air out at a given CFM overcoming the wall resistance given in terms of Pa/inches of water ?

 

[russ_watters]

Does that mean that fan charts tell what CFM flow will the fan be able to give at a given resistance to its inflow?
The resistance coming from a pipe wall for example, a fan at the outlet will be able to suck the air out at a given CFM overcoming the wall resistance given in terms of Pa/inches of water ?

Yes, the fan curve alone won't tell you the performance of the fan, just the performance range. To find the actual performance you need to match the fan curve to the system resistance.

 

[hali24953]

oooooooooo thanks!